1. Field of the Invention
The present invention relates to an ophthalmic measuring method and apparatus that can be used to screen dry eye and evaluate dry eye severity in a subject's eye.
2. Description of the Prior Art
The recent increase in the number of patients with dry eye is considered to be caused by an increased number of workers at VDTs (Visual Display Terminal), contact lens wearers or the dryness of air-conditioned rooms. Disorders in the corneal epithelium, conjunctival epithelium, and various other ophthalmic disorders can occur in conjunction with dry eye, and the diagnosis of dry eye has become an important subject of ophthalmic field.
Configurations have been proposed in the past for an ophthalmic apparatus for capturing an image of the lachrymal fluid layer of a subject's eye and observing, analyzing, and measuring the image in order to quantitatively evaluate conditions of dry eye.
Embodiments of known techniques include a technique (see Japanese Laid-open Patent Application Publication No. 1997-201334) for capturing an image of an interference pattern formed in the lachrymal fluid surface layer of a subject's eye, and evaluating dry eye conditions based on the hue of a plurality of areas in the image of the interference pattern; and a technique (see Japanese Laid-open Patent Application Publication No. 1999-267102) for projecting an image of an aperture having a prescribed shape onto the surface of lachrymal fluid accumulated in the lachrymal fluid meniscus along the lower eyelid, capturing an image of the aperture projected on the lachrymal fluid surface, finding the curvature radius of the lachrymal fluid surface from the magnification factor of the aperture image, and evaluating dry eye severity.
In the conventional techniques, particularly the technique described in Japanese Laid-open Patent Application Publication No. 1997-201334, an image of the interference color of the lachrymal fluid layer is captured, and the image is observed, analyzed, and measured, but almost no interference color occurs in the normal eye and the eye experiencing the worst severity of dry eye, and this conventional technique suffers from drawbacks in that the normal eye or the eye experiencing the worst severity of dry eye cannot be observed, analyzed, and measured.
In view of the foregoing drawbacks, an object of the present invention is to ensure that the movement speed of lachrymal fluid can be reliably measured, diagnosis can be quantitatively performed from the movement speed of the lachrymal fluid thus measured even on a severely dry eye, and the state of a normal eye can be reliably identified.